1. Field of the Invention
The present invention relates to a welding wire for joining different materials, in particular, cast iron and stainless steel, and to a vehicle component manufactured using the welding wire.
2. Background Art
In vehicles, exhaust gas temperature is increased in proportion to the gasoline mileage. Generally, the exhaust gas temperature of a vehicle provided with a turbo engine or a GDI (Gasoline Direct Injection) engine is hot to the range of about 850˜950° C., and vehicle makers have recently tried to further increase the exhaust gas temperature up to about 950˜970° C.
The exhaust manifold of an engine exhaust system through which exhaust gas is passed is a component requiring high temperature properties, in particular, heat resistance, fatigue resistance and oxidation resistance, and the magnitude of a load applied thereto is gradually increased in proportion to increases in the exhaust gas temperature. Typically, an exhaust manifold used under conditions of an exhaust temperature of 800° C. or lower is manufactured through casting using nodular graphite cast iron, and an exhaust manifold (hereinafter, referred to as “high-temperature exhaust manifold”) used at temperatures higher than the above temperature is suitably manufactured by subjecting a stainless steel sheet to pressing and then welding.
Stainless steel is much lighter than cast iron and has superior high-temperature properties, but is expensive. In order to reduce the cost, part of the high-temperature exhaust manifold is made using cast iron instead of stainless steel. Accordingly, and with reference to FIGS. 1A and 1B, a runner 21 and a flange 22, which are connected to an engine (not shown), are made of cast iron, whereas a diffuser 11 is made of stainless steel. Further, a stainless steel part 10 and a cast iron part 20 are welded to each other, thus suitably manufacturing a single exhaust manifold.
However, in the exhaust manifold thus manufactured, shortly after the welding process, solidification cracks or hot cracks (FIG. 1B) occur frequently in the joint, in particular, in the weld zone 30, of the exhaust manifold in which the stainless steel part 10 and the cast iron part 20 are joined to each other. Such a cracked portion or a weak portion causes leakage of the exhaust gas or may result in rupture.
The above information disclosed in this the Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.